Temperable electrochromic devices

ABSTRACT

This disclosure provides systems, methods, and apparatus for tempering or chemically strengthening glass substrates having electrochromic devices fabricated thereon. In one aspect, an electrochromic device is fabricated on a glass substrate. The glass substrate is then tempered or chemically strengthened. The disclosed methods may reduce or prevent potential issues that the electrochromic device may experience during the tempering or the chemical strengthening processes, including the loss of charge carrying ions from the device, redistribution of charge carrying ions in the device, modification of the morphology of materials included in the device, modification of the oxidation state of materials included in the device, and the formation of an interfacial region between the electrochromic layer and the counter electrode layer of the device that impacts the performance of the device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application numberUS2012/043385 (designating the United States), filed on Jun. 20, 2012and titled “TEMPERABLE ELECTROCHROMIC DEVICES,” which claims benefit ofU.S. Provisional Patent Application Ser. No. 61/499,618, filed on Jun.21, 2011 and titled “TEMPERABLE ELECTROCHROMIC DEVICES,” each of whichare hereby incorporated by reference in their entireties and for allpurposes. This application is also a continuation-in-part of U.S. patentapplication Ser. No. 12/645,111, titled “FABRICATION OF LOW DEFECTIVITYELECTROCHROMIC DEVICES,” filed on Dec. 22, 2009, which claims benefit ofU.S. Provisional Patent Application Ser. No. 61/165,484, filed on Mar.31, 2009 and titled “All-Solid-State Electrochromic Device,” each ofwhich are hereby incorporated by reference in their entireties and forall purposes.

FIELD

The present disclosure concerns temperable electrochromic devices andrelated methods.

BACKGROUND

Glass tempering is a process by which glass is thermally treated toincrease its strength. During tempering the glass is subjected to highheat until its softening point is reached and then the glass is rapidlycooled. This creates a tension zone in the interior of the glass, whichis surrounded by a compression zone. These zones contribute to highstress within tempered glass. Glass generally needs to be cut or groundto a desired geometry before tempering, because, once tempered, theglass cannot be cut or it will suffer catastrophic breakage into smallpieces due to the high stress imparted in the glass during tempering.

Conventionally, electronic devices, such as electrochromic devices, arefabricated on tempered glass. The desired size of glass is chosen; theglass is tempered and only then is the electronic device fabricatedthereon. Thus, if a device is fabricated on a glass substrate and thenthe glass substrate is tempered, the device would be exposed to thetempering process. Conventionally, this process destroys functionalityof the device.

SUMMARY

This disclosure provides systems, methods, and apparatus for temperingor chemically strengthening glass substrates having electrochromicdevices fabricated thereon. In one aspect, an electrochromic device isfabricated on a glass substrate. The glass substrate is then tempered orchemically strengthened. The disclosed methods may reduce or preventpotential issues that the electrochromic device may experience duringthe tempering or the chemical strengthening processes.

One aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic deviceon a glass substrate and then tempering the glass substrate by heatingthe glass substrate.

Another aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic deviceon a glass substrate and then strengthening the glass substrate with achemical process.

Another aspect of the subject matter described in this disclosure can beimplemented in a method of forming an EC device on a chemicallystrengthened pane. The method includes coating an annealed glass panewith potassium nitrate and coating the annealed glass pane with an ECdevice including a layer at the interface between the potassium nitrateand the EC device. The layer protects the EC device from intrusion bypotassium ions. The EC device and the annealed glass pane are thenheated to between about 300° C. and about 400° C.

Another aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic deviceon a glass substrate. The electrochromic device includes more lithiumthan needed for a functional electrochromic device. The electrochromicdevice further includes a first transparent conducting oxide layerdisposed on the substrate, a stack disposed on the first transparentconducting oxide layer, and a second transparent conducting oxide layerdisposed on top of the stack. The stack includes an electrochromic layercomprising an electrochromic material and a counter electrode layercomprising a counter electrode material. The glass substrate is thentempered.

Another aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic deviceon a glass substrate. The electrochromic device includes a firsttransparent conducting oxide layer disposed on the substrate, a stackdisposed on the first transparent conducting oxide layer, and a secondtransparent conducting oxide layer disposed on top of the stack. Thestack includes an electrochromic layer comprising an electrochromicmaterial and a counter electrode layer comprising a counter electrodematerial. Lithium ions in the electrochromic device are driven into theelectrochromic layer, the counter electrode layer, and/or a regionbetween the electrochromic layer and the counter electrode layer. Afterdriving the lithium ions, the glass substrate is tempered.

Another aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic devicedisposed on a glass substrate, providing a lithium source disposed on asurface of the electrochromic device, and tempering the glass substrate.

Another aspect of the subject matter described in this disclosure can beimplemented in a method including fabricating an electrochromic deviceon a glass substrate, providing a lithium diffusion barrier on a surfaceof the electrochromic device, and tempering the glass substrate.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description can be more fully understood whenconsidered in conjunction with the drawings in which:

FIGS. 1A-1C show schematic diagrams of electrochromic devices formed onglass substrates, i.e., electrochromic lites.

FIGS. 2A and 2B show cross-sectional schematic diagrams of theelectrochromic lites as described in relation to FIGS. 1A-C integratedinto an IGU.

FIG. 3A depicts a schematic cross-section of an electrochromic device.

FIG. 3B depicts a schematic cross-section of an electrochromic device ina bleached state (or transitioning to a bleached state).

FIG. 3C depicts a schematic cross-section of the electrochromic deviceshown in FIG. 3B, but in a colored state (or transitioning to a coloredstate).

FIG. 4 shows a flow chart of a method for fabricating a portion of anIGU.

FIGS. 5A and 5B show tables summarizing some of the differentembodiments disclosed herein.

DETAILED DESCRIPTION Introduction

As described in U.S. patent application Ser. No. 12/941,882, filed Nov.8, 2010, which is incorporated herein by reference in its entirety, itwould be desirable to temper glass after an electrochromic device isformed thereon. In this way, electrochromic lites of varying sizes canbe cut from a large-format non-tempered glass sheet and then theindividual lites tempered. By tempering the EC lites after cutting themto desired sizes, the quality and the yield are enhanced because onlythose lites of high quality, for example, low defectivity, are chosenfor the tempering process. This saves considerable energy because onlythe most desirable lites go through the tempering furnace, rather thantempering many lites and then choosing the best lites from the temperedlot.

The tempering of glass is typically conducted at a high temperature fora sufficient period of time that it may cause damage to or degradationof the electrochromic device. Typically, tempering is performed at atemperature above 600° C., for example, about 680° C., for severalminutes. This heating process is followed by a very rapid quench whichpreserves internal stresses within the glass pane that were created bythe heating. In some cases, solid state electrochromic devices arefabricated on a glass substrate which may begin to degrade over timewhen heated beyond about 350° C.

Among the potential problems that an electrochromic device mightexperience during tempering are (1) the loss of lithium or other chargecarrying ion from the device, (2) the redistribution of lithium or othercharge carrying ion within the device, (3) the modification of themorphology of one or more layers of the device by, for example,increasing the grain size of an electrochromic active layer, (4) themodification of the oxidation state of one or more materials in theelectrochromic stack by, for example, the diffusion of oxygen into thedevice, out of the device, or within the device, and (5) the formationof an ion conducting layer or interfacial region between theelectrochromic and counter electrode layers to a thickness thatnegatively impacts performance.

In this disclosure, various processing techniques are described whichpermit forming an electrochromic device on a glass substrate prior totempering the glass substrate. Described are techniques to mitigate orameliorate the damage or degradation that would otherwise occur to theelectrochromic device during tempering. Thus, for example, devices arefabricated in order to minimize damage that tempering would otherwiseimpose on the devices, and/or the devices are fabricated to takeadvantage of the tempering conditions so that tempering yields liteswith functional EC devices thereon. In some embodiments, the tempered EClites are further processed in order to optimize their performance.

In this regard, many approaches to forming electrochromic devices aredescribed. Certain suitable processes are described in U.S. patentapplication Ser. No. 12/645,111, filed Dec. 22, 2009, U.S. patentapplication Ser. No. 12/645,159, filed Dec. 22, 2009, and U.S. patentapplication Ser. No. 12/772,075, filed Apr. 30, 2010. Each of thesedisclosures is relevant and presents fabrication methods that may serveas baseline processes. Each of these patent applications is incorporatedherein by reference in its entirety.

It should be understood that some of the process variations describedherein may be extended to protecting devices other than electrochromicdevices that might be formed on a glass substrate prior to tempering.For convenience, electrochromic devices will be used as the example inthe following discussion. Certain all solid state electrochromic devicesare often made from metal oxides, ceramics, and the like, i.e.,materials that can withstand the tempering process; such all solid statedevices are particularly well suited for methods described herein.Organic electrochromic materials tend not to be robust enough to survivetempering.

It should also be understood that the tempering process may be performedin line with or as part of the electrochromic device fabricationprocess. For example, a pane of glass may be passed through successivedeposition stations where each station deposits some or all of aparticular layer in the electrochromic device stack. Often, thesestations will create the stack layers by a physical vapor deposition(PVD) process, which may be a plasma assisted process. One or more ofthe stations may also anneal the partially or completely fabricateddevice. Besides a conventional anneal, the stations may be configured tocarry out a multistep thermochemical conditioning (MTCC), as describedin U.S. patent application Ser. No. 12/772,055, filed on Apr. 30, 2010,entitled “Electrochromic Devices,” naming Zhongchun Wang et al. asinventors, which is herein incorporated by reference. In accordance withvarious embodiments disclosed herein, one or more of the annealoperations normally performed in an electrochromic device fabricationprocess is dispensed with in favor of accomplishing the same physicaltransformation(s) during a downstream tempering process.

In some embodiments, the electrochromic device is first formed on theglass pane by a process such as that described herein and then temperingis conducted in a separate operation, e.g., after the glass pane onwhich the electrochromic device structure is formed is cut into one ormore smaller panes sized for commercial products.

Overview of Electrochromic Devices

In order to orient the reader to the embodiments of systems, methods,and apparatus disclosed herein, a brief discussion of electrochromicdevices is provided. This initial discussion of electrochromic devicesis provided for context only, and the subsequently described embodimentsof systems, methods, and apparatus are not limited to the specificfeatures and fabrication processes of this initial discussion.

A particular example of an electrochromic lite is described withreference to FIGS. 1A-1C, in order to illustrate embodiments describedherein. FIG. 1A is a cross-sectional representation (see cut X-X′ ofFIG. 1C) of an electrochromic lite, 100, which is fabricated startingwith a glass sheet, 105. Lite 100 includes glass sheet 105 andfabricated thereon a diffusion barrier 110, e.g., a sodium diffusionbarrier which blocks sodium ions in the glass from migrating to thedevice. On the diffusion barrier is a first transparent conductive oxide(TCO), 115, e.g., a fluorinated tin oxide, indium tin oxide, or similartransparent conducting material. Second TCO, 130, is the top layer. Inbetween the TCOs are EC stack, 125, which can be, e.g., three layersincluding an electrochromic layer (EC), an ion-conducting (IC)electrically-insulating layer, and a counter electrode layer which mayserve as an ion storage layer and also a complimentary coloring layer tothe EC layer.

FIG. 1B shows an end view (see perspective Y-Y′ of FIG. 1C) of EC lite100, and FIG. 1C shows a top-down view of EC lite 100. FIG. 1A shows theelectrochromic lite after fabrication on glass sheet 105, edge deletedto produce area, 140, around the perimeter of the lite. Theelectrochromic lite has also been laser scribed and bus bars have beenattached. In this example, the edge deletion process removes both TCO115 and diffusion barrier 110, but in other embodiments only the TCO isremoved, leaving the diffusion barrier intact. The TCO 115 is the firstof two conductive layers used to form the electrodes of theelectrochromic device fabricated on the glass sheet. In this example,the glass sheet includes underlying glass and the diffusion barrierlayer. Thus, in this example, the diffusion barrier is formed, and thenthe first TCO, an EC stack, 125, (for example, having electrochromic,ion conductor, and counter electrode layers), and a second TCO, 130, areformed. In one embodiment, the electrochromic device (EC stack andsecond TCO) is fabricated in an integrated deposition system where theglass sheet does not leave the integrated deposition system at any timeduring fabrication of the stack. In one embodiment, the first TCO layeris also formed using the integrated deposition system where the glasssheet does not leave the integrated deposition system during depositionof the EC stack and the (second) TCO layer. In one embodiment, all ofthe layers (diffusion barrier, first TCO, EC stack, and second TCO) aredeposited in the integrated deposition system where the glass sheet doesnot leave the integrated deposition system during deposition. In thisexample, prior to deposition of EC stack 125, an isolation trench, 120,is cut through TCO 115 and diffusion barrier 110. Trench 120 is made incontemplation of electrically isolating an area of TCO 115 that willreside under bus bar 1 after fabrication is complete (see FIG. 1A). Thisis done to avoid charge buildup and coloration of the EC device underthe bus bar, which can be undesirable.

After formation of the EC device, edge deletion processes and additionallaser scribing are performed. FIG. 1A depicts areas 140 where the devicehas been removed, in this example, from a perimeter region surroundinglaser scribe trenches, 150, 155, 160, and 165. Trenches 150, 160 and 165pass through the EC stack and also through the first TCO and diffusionbarrier. Trench 155 passes through second TCO 130 and the EC stack, butnot the first TCO 115. Laser scribe trenches 150, 155, 160, and 165 aremade to isolate portions of the EC device, 135, 145, 170, and 175, whichwere potentially damaged during edge deletion processes from theoperable EC device. In this example, laser scribe trenches 150, 160, and165 pass through the first TCO to aid in isolation of the device (laserscribe trench 155 does not pass through the first TCO, otherwise itwould cut off bus bar 2's electrical communication with the first TCOand thus the EC stack). The laser or lasers used for the laser scribeprocesses are typically, but not necessarily, pulse-type lasers, forexample, diode-pumped solid state lasers. For example, the laser scribeprocesses can be performed using a suitable laser from IPG Photonics (ofOxford, Mass.), or from Ekspla (of Vilnius, Lithuania). Scribing canalso be performed mechanically, for example, by a diamond tipped scribe.One of ordinary skill in the art would appreciate that the laserscribing processes can be performed at different depths and/or performedin a single process whereby the laser cutting depth is varied, or not,during a continuous path around the perimeter of the EC device. In oneembodiment, the edge deletion is performed to the depth of the firstTCO.

After laser scribing is complete, bus bars are attached. Non-penetratingbus bar (1) is applied to the second TCO. Non-penetrating bus bar (2) isapplied to an area where the device was not deposited (for example, froma mask protecting the first TCO from device deposition), in contact withthe first TCO or, in this example, where an edge deletion process (forexample, laser ablation using an apparatus having a XY or XYZgalvanometer) was used to remove material down to the first TCO. In thisexample, both bus bar 1 and bus bar 2 are non-penetrating bus bars. Apenetrating bus bar is one that is typically pressed into and throughthe EC stack to make contact with the TCO at the bottom of the stack. Anon-penetrating bus bar is one that does not penetrate into the EC stacklayers, but rather makes electrical and physical contact on the surfaceof a conductive layer, for example, a TCO.

The TCO layers can be electrically connected using a non-traditional busbar, for example, a bus bar fabricated with screen and lithographypatterning methods. In one embodiment, electrical communication isestablished with the device's transparent conducting layers via silkscreening (or using another patterning method) a conductive ink followedby heat curing or sintering the ink. Advantages to using the abovedescribed device configuration include simpler manufacturing, forexample, and less laser scribing than conventional techniques which usepenetrating bus bars.

After the bus bars are connected, the device is integrated into aninsulated glass unit (IGU), which includes, for example, wiring the busbars and the like. In some embodiments, one or both of the bus bars areinside the finished IGU, however in one embodiment one bus bar isoutside the seal of the IGU and one bus bar is inside the IGU. In theformer embodiment, area 140 is used to make the seal with one face ofthe spacer used to form the IGU. Thus, the wires or other connection tothe bus bars runs between the spacer and the glass. As many spacers aremade of metal, for example, stainless steel, which is conductive, it isdesirable to take steps to avoid short circuiting due to electricalcommunication between the bus bar and connector thereto and the metalspacer.

As described above, after the bus bars are connected, the electrochromiclite is integrated into an IGU, which includes, for example, wiring forthe bus bars and the like. In the embodiments described herein, both ofthe bus bars are inside the primary seal of the finished IGU. FIG. 2Ashows a cross-sectional schematic diagram of the electrochromic windowas described in relation to FIGS. 1A-C integrated into an IGU, 200. Aspacer, 205, is used to separate the electrochromic lite from a secondlite, 210. Second lite 210 in IGU 200 is a non-electrochromic lite,however, the embodiments disclosed herein are not so limited. Forexample, lite 210 can have an electrochromic device thereon and/or oneor more coatings such as low-E coatings and the like. Lite 201 can alsobe laminated glass, such as depicted in FIG. 2B (lite 201 is laminatedto reinforcing pane, 230, via resin, 235). Between spacer 205 and thefirst TCO layer of the electrochromic lite is a primary seal material,215. This primary seal material is also between spacer 205 and secondglass lite 210. Around the perimeter of spacer 205 is a secondary seal,220. Bus bar wiring/leads traverse the seals for connection to acontroller. Secondary seal 220 may be much thicker that depicted. Theseseals aid in keeping moisture out of an interior space, 225, of the IGU.They also serve to prevent argon or other gas in the interior of the IGUfrom escaping.

FIG. 3A schematically depicts an electrochromic device, 300, incross-section. Electrochromic device 300 includes a substrate, 302, afirst conductive layer (CL), 304, an electrochromic layer (EC), 306, anion conducting layer (IC), 308, a counter electrode layer (CE), 310, anda second conductive layer (CL), 314. Layers 304, 306, 308, 310, and 314are collectively referred to as an electrochromic stack 320. A voltagesource 316 operable to apply an electric potential across electrochromicstack 320 effects the transition of the electrochromic device from, forexample, a bleached state to a colored state (depicted). The order oflayers can be reversed with respect to the substrate.

Electrochromic devices having distinct layers as described can befabricated as all solid state devices and/or all inorganic deviceshaving low defectivity. Such devices and methods of fabricating them aredescribed in more detail in U.S. patent application Ser. No. 12/645,111,entitled, “Fabrication of Low-Defectivity Electrochromic Devices,” filedon Dec. 22, 2009 and naming Mark Kozlowski et al. as inventors, and inU.S. patent application Ser. No. 12/645,159, entitled, “ElectrochromicDevices,” filed on Dec. 22, 2009 and naming Zhongchun Wang et al. asinventors, both of which are incorporated by reference herein for allpurposes. It should be understood, however, that any one or more of thelayers in the stack may contain some amount of organic material. Thesame can be said for liquids that may be present in one or more layersin small amounts. It should also be understood that solid state materialmay be deposited or otherwise formed by processes employing liquidcomponents such as certain processes employing sol-gels or chemicalvapor deposition.

Additionally, it should be understood that the reference to a transitionbetween a bleached state and colored state is non-limiting and suggestsonly one example, among many, of an electrochromic transition that maybe implemented. Unless otherwise specified herein (including theforegoing discussion), whenever reference is made to a bleached-coloredtransition, the corresponding device or process encompasses otheroptical state transitions such as non-reflective-reflective,transparent-opaque, etc. Further, the term “bleached” refers to anoptically neutral state, for example, uncolored, transparent, ortranslucent. Still further, unless specified otherwise herein, the“color” of an electrochromic transition is not limited to any particularwavelength or range of wavelengths. As understood by those of skill inthe art, the choice of appropriate electrochromic and counter electrodematerials governs the relevant optical transition.

In embodiments described herein, the electrochromic device reversiblycycles between a bleached state and a colored state. In some cases, whenthe device is in a bleached state, a potential is applied to theelectrochromic stack 320 such that available ions in the stack resideprimarily in the counter electrode 310. When the potential on theelectrochromic stack is reversed, the ions are transported across theion conducting layer 308 to the electrochromic material 306 and causethe material to transition to the colored state.

Referring again to FIG. 3A, voltage source 316 may be configured tooperate in conjunction with radiant and other environmental sensors. Asdescribed herein, voltage source 316 interfaces with a device controller(not shown in this figure). Additionally, voltage source 316 mayinterface with an energy management system that controls theelectrochromic device according to various criteria such as the time ofyear, time of day, and measured environmental conditions. Such an energymanagement system, in conjunction with large area electrochromic devices(for example, an electrochromic window), can dramatically lower theenergy consumption of a building.

Any material having suitable optical, electrical, thermal, andmechanical properties may be used as substrate 302. Such substratesinclude, for example, glass, plastic, and mirror materials. Suitableglasses include either clear or tinted soda lime glass, including sodalime float glass. The glass may be tempered or untempered.

In many cases, the substrate is a glass pane sized for residentialwindow applications. The size of such glass pane can vary widelydepending on the specific needs of the residence. In other cases, thesubstrate is architectural glass. Architectural glass is typically usedin commercial buildings, but may also be used in residential buildings,and typically, though not necessarily, separates an indoor environmentfrom an outdoor environment. In certain embodiments, architectural glassis at least 20 inches by 20 inches, and can be much larger, for example,as large as about 80 inches by 120 inches. Architectural glass istypically at least about 2 mm thick, typically between about 3 mm andabout 6 mm thick. Of course, electrochromic devices are scalable tosubstrates smaller or larger than architectural glass. Further, theelectrochromic device may be provided on a mirror of any size and shape.

On top of substrate 302 is conductive layer 304. In certain embodiments,one or both of the conductive layers 304 and 314 is inorganic and/orsolid. Conductive layers 304 and 314 may be made from a number ofdifferent materials, including conductive oxides, thin metalliccoatings, conductive metal nitrides, and composite conductors.Typically, conductive layers 304 and 314 are transparent at least in therange of wavelengths where electrochromism is exhibited by theelectrochromic layer. Transparent conductive oxides include metal oxidesand metal oxides doped with one or more metals. Examples of such metaloxides and doped metal oxides include indium oxide, indium tin oxide,doped indium oxide, tin oxide, doped tin oxide, zinc oxide, aluminumzinc oxide, doped zinc oxide, ruthenium oxide, doped ruthenium oxide andthe like. Since oxides are often used for these layers, they aresometimes referred to as “transparent conductive oxide” (TCO) layers.Thin metallic coatings that are substantially transparent may also beused.

The function of the conductive layers is to spread an electric potentialprovided by voltage source 316 over surfaces of the electrochromic stack320 to interior regions of the stack, with relatively little ohmicpotential drop. The electric potential is transferred to the conductivelayers though electrical connections to the conductive layers. In someembodiments, bus bars, one in contact with conductive layer 304 and onein contact with conductive layer 314, provide the electric connectionbetween the voltage source 316 and the conductive layers 304 and 314.The conductive layers 304 and 314 may also be connected to the voltagesource 316 with other conventional means.

Overlaying conductive layer 304 is electrochromic layer 306. In someembodiments, electrochromic layer 306 is inorganic and/or solid. Theelectrochromic layer may contain any one or more of a number ofdifferent electrochromic materials, including metal oxides. Such metaloxides include tungsten oxide (WO₃), molybdenum oxide (MoO₃), niobiumoxide (Nb₂O₅), titanium oxide (TiO₂), copper oxide (CuO), iridium oxide(Ir₂O₃), chromium oxide (Cr₂O₃), manganese oxide (Mn₂O₃), vanadium oxide(V₂O₅), nickel oxide (Ni₂O₃), cobalt oxide (Co₂O₃) and the like. Duringoperation, electrochromic layer 306 transfers ions to and receives ionsfrom counter electrode layer 310 to cause optical transitions.

Generally, the colorization (or change in any optical property—forexample, absorbance, reflectance, and transmittance) of theelectrochromic material is caused by reversible ion insertion into thematerial (for example, intercalation) and a corresponding injection of acharge balancing electron. Typically some fraction of the ionsresponsible for the optical transition is irreversibly bound up in theelectrochromic material. Some or all of the irreversibly bound ions areused to compensate “blind charge” in the material. In mostelectrochromic materials, suitable ions include lithium ions (Li⁺) andhydrogen ions (H⁺) (that is, protons). In some cases, however, otherions will be suitable. In various embodiments, lithium ions are used toproduce the electrochromic phenomena. Intercalation of lithium ions intotungsten oxide (WO_(3-y) (0<y≦˜0.3)) causes the tungsten oxide to changefrom transparent (bleached state) to blue (colored state).

Referring again to FIG. 3A, in electrochromic stack 320, ion conductinglayer 308 is sandwiched between electrochromic layer 306 and counterelectrode layer 310. In some embodiments, counter electrode layer 310 isinorganic and/or solid. The counter electrode layer may comprise one ormore of a number of different materials that serve as a reservoir ofions when the electrochromic device is in the bleached state. During anelectrochromic transition initiated by, for example, application of anappropriate electric potential, the counter electrode layer transferssome or all of the ions it holds to the electrochromic layer, changingthe electrochromic layer to the colored state. Concurrently, in the caseof NiWO, the counter electrode layer colors with the loss of ions.

In some embodiments, suitable materials for the counter electrodecomplementary to WO₃ include nickel oxide (NiO), nickel tungsten oxide(NiWO), nickel vanadium oxide, nickel chromium oxide, nickel aluminumoxide, nickel manganese oxide, nickel magnesium oxide, chromium oxide(Cr₂O₃), manganese oxide (MnO₂), and Prussian blue.

When charge is removed from a counter electrode 310 made of nickeltungsten oxide (that is, ions are transported from counter electrode 310to electrochromic layer 306), the counter electrode layer willtransition from a transparent state to a colored state.

In the depicted electrochromic device, between electrochromic layer 306and counter electrode layer 310, there is the ion conducting layer 308.Ion conducting layer 308 serves as a medium through which ions aretransported (in the manner of an electrolyte) when the electrochromicdevice transitions between the bleached state and the colored state.Preferably, ion conducting layer 308 is highly conductive to therelevant ions for the electrochromic and the counter electrode layers,but has sufficiently low electron conductivity that negligible electrontransfer takes place during normal operation. A thin ion conductinglayer with high ionic conductivity permits fast ion conduction and hencefast switching for high performance electrochromic devices. In certainembodiments, the ion conducting layer 308 is inorganic and/or solid.

Examples of suitable ion conducting layers (for electrochromic deviceshaving a distinct IC layer) include silicates, silicon oxides, tungstenoxides, tantalum oxides, niobium oxides, and borates. These materialsmay be doped with different dopants, including lithium. Lithium dopedsilicon oxides include lithium silicon-aluminum-oxide. In someembodiments, the ion conducting layer comprises a silicate-basedstructure. In some embodiments, a silicon-aluminum-oxide (SiAlO) is usedfor the ion conducting layer 308.

Electrochromic device 300 may include one or more additional layers (notshown), such as one or more passive layers. Passive layers used toimprove certain optical properties may be included in electrochromicdevice 300. Passive layers for providing moisture or scratch resistancemay also be included in electrochromic device 300. For example, theconductive layers may be treated with anti-reflective or protectiveoxide or nitride layers. Other passive layers may serve to hermeticallyseal electrochromic device 300.

FIG. 3B is a schematic cross-section of an electrochromic device in ableached state (or transitioning to a bleached state). In accordancewith specific embodiments, an electrochromic device, 400, includes atungsten oxide electrochromic layer (EC), 406, and a nickel-tungstenoxide counter electrode layer (CE), 410. Electrochromic device 400 alsoincludes a substrate, 402, a conductive layer (CL), 404, an ionconducting layer (IC), 408, and conductive layer (CL), 414.

A power source, 416, is configured to apply a potential and/or currentto an electrochromic stack, 420, through suitable connections (forexample, bus bars) to the conductive layers, 404 and 414. In someembodiments, the voltage source is configured to apply a potential of afew volts in order to drive a transition of the device from one opticalstate to another. The polarity of the potential as shown in FIG. 3A issuch that the ions (lithium ions in this example) primarily reside (asindicated by the dashed arrow) in nickel-tungsten oxide counterelectrode layer 410.

FIG. 3C is a schematic cross-section of electrochromic device 400 shownin FIG. 3B but in a colored state (or transitioning to a colored state).In FIG. 3C, the polarity of voltage source 416 is reversed, so that theelectrochromic layer is made more negative to accept additional lithiumions, and thereby transition to the colored state. As indicated by thedashed arrow, lithium ions are transported across ion conducting layer408 to tungsten oxide electrochromic layer 406. Tungsten oxideelectrochromic layer 406 is shown in the colored state. Nickel-tungstenoxide counter electrode 410 is also shown in the colored state. Asexplained, nickel-tungsten oxide becomes progressively more opaque as itgives up (deintercalates) lithium ions. In this example, there is asynergistic effect where the transition to colored states for bothlayers 406 and 410 are additive toward reducing the amount of lighttransmitted through the stack and substrate.

As described above, an electrochromic device may include anelectrochromic (EC) electrode layer and a counter electrode (CE) layerseparated by an ionically conductive (IC) layer that is highlyconductive to ions and highly resistive to electrons. As conventionallyunderstood, the ionically conductive layer therefore prevents shortingbetween the electrochromic layer and the counter electrode layer. Theionically conductive layer allows the electrochromic and counterelectrodes to hold a charge and thereby maintain their bleached orcolored states. In electrochromic devices having distinct layers, thecomponents form a stack which includes the ion conducting layersandwiched between the electrochromic electrode layer and the counterelectrode layer. The boundaries between these three stack components aredefined by abrupt changes in composition and/or microstructure. Thus,the devices have three distinct layers with two abrupt interfaces.

In accordance with certain embodiments, the counter electrode andelectrochromic electrodes are formed immediately adjacent one another,sometimes in direct contact, without separately depositing an ionicallyconducting layer. In some embodiments, electrochromic devices having aninterfacial region rather than a distinct IC layer are employed. Suchdevices, and methods of fabricating them, are described in U.S. patentapplication Ser. Nos. 12/772,055 and 12/772,075, each filed on Apr. 30,2010, and in U.S. patent application Ser. Nos. 12/814,277 and12/814,279, each filed on Jun. 11, 2010—each of the four applications isentitled “Electrochromic Devices,” each names Zhongchun Wang et al. asinventors, and each is incorporated by reference herein in its entirety.

In some embodiments, an electrochromic device includes a single layergraded composition including an EC region, an IC region, and a CEregion, respectively. Such a single layer graded composition may becalled an EC element. In certain embodiments, the EC element is allsolid-state and inorganic. The EC element functions as an EC device, butis a single layer, not multiple layers, one stacked upon the other, asin conventional practice. In certain embodiments, the EC elementincludes transition metal oxides, alkali metals, and mixed transitionmetal oxides. One embodiment is an EC device including a firsttransparent electrode, a second transparent electrode, and the ECelement sandwiched in between the first and second transparentelectrodes. In one embodiment, an EC element includes transparentconducting regions as well, i.e., a fully functioning EC element that isa single coating on a substrate, the single layer having gradedfunctional regions within it. EC elements are further described in U.S.patent application Ser. No. 13/462,725, filed on May 2, 2012, which isincorporated by reference herein in its entirety. In some embodiments,tempering the glass substrate may aid in forming the graded compositionof an EC element. In some embodiments, an EC element may be less proneto damage during the tempering processes described herein. For example,an EC device including a distinct electrochromic layer, a distinct ionconducting layer, and a distinct counter electrode layer may be prone todamage during tempering due to different thermal expansion coefficientsof each of the layers. An EC element, being a single graded layer, i.e.,not having these distinct boundaries between layers, does not experienceshearing forces between sub-layers because there are no distinctboundaries between sublayers in an EC element. One embodiment is amethod of forming a functional EC element on a glass sheet, the methodincluding fabricating the EC element on the glass sheet and thentempering the glass sheet.

Overview of Fabricating a Portion of an IGU Including an ElectrochromicDevice

FIG. 4 shows a flow chart of a method for fabricating a portion of anIGU. For example, a method, 500, shown in FIG. 4 may be used tofabricate a pane, including an electrochromic device, of an IGU.Starting at operation 510 of method 500, an electrochromic device isfabricated on a glass substrate. Typically, an electrochromic device isfabricated on a large glass substrate that is intended to be cut intosmaller panes at a later stage of the process. For example, the glasssubstrate may be a piece of glass of between about 3 meters and about 6meters in length on at least one side. In some cases, the glasssubstrate is rectangular, being about 3 to 6 meters high and about 1.5to 3 meters wide. In a specific embodiment, the glass substrate is about2 meters wide and about 3 meters high. In one embodiment, the glasssubstrate is about six feet by ten feet. Suitable glass for the glasssubstrate includes float glass, Gorilla® Glass (a trade name foralkali-aluminosilicate sheet glass available from Dow Corning, Corp. ofMidland, Mich.) and the like.

In one embodiment, the glass substrate is float glass, optionally coatedwith a transparent conducting oxide (TCO) and a diffusion barrier layer.Examples of such glasses include conductive layer coated glasses soldunder the trademark TEC® Glass by Pilkington, of Toledo, Ohio andSUNGATE® 300 and SUNGATE® 500 by PPG Industries of Pittsburgh, Pa. Theglass substrate has a size that is at least equal to the largest ECglass pane contemplated for manufacture. TEC® Glass is a glass coatedwith a fluorinated tin oxide conductive layer. Such glass typically alsohas a diffusion barrier layer between the TCO and the float glass toprevent sodium from diffusing from the glass into the TCO. In oneembodiment, the glass substrate does not have a preformed TCO ordiffusion barrier on it, for example, in one embodiment the diffusionbarrier, a first TCO, an electrochromic stack and a second TCO are allformed in a single apparatus under a controlled ambient environment.

For the fabrication of the electrochromic device, in the event that theglass sheet includes a preformed diffusion barrier and TCO, then theelectrochromic device uses the TCO as one of its conductors. In theevent the glass sheet is float glass without any preformed coatings,then operation 510 may involve initially depositing a diffusion barrierlayer, then a transparent conductor (typically a TCO) layer, andthereafter the remainder of the electrochromic device is formed. Thisincludes an electrochromic stack having an electrochromic (EC) layer, acounter electrode (CE) layer and an ion conducting (IC) layer. Afterforming the electrochromic stack, another transparent conductor layer(typically a TCO layer) is deposited as a second conductor (to deliverpower to the EC stack). At this point, the electrochromic device iscompleted and operation 510 is concluded. One or more capping layers mayalso be applied. In one example, a hermetic layer is applied to keepmoisture out of the device. In another example, a low-E (emissivity)coating is applied.

In operation 520, the glass substrate is cut according to a pattern tocreate one or more electrochromic panes. In some embodiments, otheroperations may occur prior to operation 520, including defining thecutting pattern, as described in U.S. patent application Ser. No.12/941,882, filed Nov. 8, 2010. The cutting can be accomplished by anysuitable process. In some cases, the cutting is accompanied by an edgefinishing operation. Mechanical cutting typically involves scoring theglass with a hard tool, such as a diamond tip on a wheel, followed bybreaking the glass along the score line. Thus, mechanical cuttingincludes “scoring” and breaking. Sometimes the term “scoring” isreferred to as “scribing” in the glass window fabrication industry.

Cutting can produce microcracks and internal stresses proximate the cut.These can result in chipping or breaking of the glass, particularly nearthe edges. To mitigate the problems produced by cutting, cut glass maybe subject to edge finishing, for example, by mechanical and/or lasermethods. Mechanical edge finishing typically involves grinding with, forexample, a grinding wheel containing clay, stone, diamond, etc.Typically, water flows over edge during mechanical edge finishing. Theresulting edge surface is relatively rounded and crack free. Laser edgefinishing typically produces a flat, substantially defect free surface.For example, an initial cut through the glass, perpendicular to thesurface of the glass, may make a substantially defect free cut. Howeverthe right angle edges at the perimeter of the glass are susceptible tobreakage due to handling. In some embodiments, a laser is usedsubsequently to cut off these 90 degree edges to produce a slightly morerounded or polygonal edge.

Examples of cutting and optional edge finishing processes include thefollowing: (1) mechanical cutting, (2) mechanical cutting and mechanicaledge finishing, (3) laser cutting, (4) laser cutting and mechanical edgefinishing, and (5) laser cutting and laser edge finishing.

In one embodiment, the panes are cut from the glass sheet in a mannerthat actually strengthens and/or improves the edge quality of theresulting panes. In a specific example, this is accomplished using laserinduced scoring by tension. In this method, a gas laser, for example aCO₂ laser with a wavelength of 10.6 micrometers, is used to heat thesurface of the glass along a cut line to produce a compressive stress inthe glass along the cut line. A cooling device, for example a gas and/orwater jet, is used to quickly cool the heated line. This causes a scoreto form in the glass along the cutting line. The glass is then brokenalong the score by, for example, a conventional mechanical breakingdevice. Using this method, the cut lines are extremely clean, that is,there are minimal if any defects in the glass that can propagate andcause further breakage due to stresses applied to the pane. In oneembodiment, the edges are subsequently mechanically and/or laserfinished to remove the 90 degree edges to create a more rounded and/orpolygonal edge.

In operation 530, an EC pane is tempered using a method as disclosedherein. Further operations, also described in U.S. patent applicationSer. No. 12/941,882, filed Nov. 8, 2010, may be performed prior toincorporating the EC pane into an IGU.

Tempering

During a thermal tempering process, a glass substrate is heated to about680° C. or higher and then quenched rapidly to increase the glassstrength. Due to the sensitivity of the EC device to high temperatures,certain embodiments include tempering methods which reduce the thermalload to the device. In one embodiment, reduction of the thermal load isachieved by localized heating of the glass substrate. In one embodiment,this localized heating is performed by infrared (IR) heating of theglass substrate including the EC device with a wavelength/frequency oflight at which the glass substrate absorbs substantially greater energythan the EC device. In another embodiment, an extremely low emissivitybottom TCO layer is used and IR energy is applied to the glass substrateon the face opposite the EC device. The IR energy impinging the layer ofthe low emissivity TCO will reflect most of the IR energy back into theglass, thus selectively heating and tempering the glass and preventingsubstantial energy transmission to the EC device.

In addition to reducing IR absorption in the EC device, the thermalconductivity between the glass and the EC device (including the bottomTCO) may be reduced during thermal tempering. However, for the EC deviceto provide a maximum energy savings benefit during operation, thethermal conductivity between the EC device and the glass should be high.In one embodiment, a variable thermal conductivity layer is formedbetween EC device and the glass. The variable thermal conductivity layeris placed in a low thermal conductivity state during the temperingprocess and placed in a high thermal conductivity state post-temperingduring normal EC device functioning. The thermal conductivity of thevariable thermal conductivity layer could be modified by an externalstimulus, such as an electrical, an optical, or an acoustic signal, etc.The variable thermal conductivity layer also could be engineered tochange thermal conductivity over time during the course of the temperingprocess.

In certain embodiments, a capping layer is used to ameliorate possiblenegative effects of tempering on the EC stack materials, including theloss of lithium due to oxidation. In one embodiment, a capping layerincludes an oxygen barrier material that prevents oxygen diffusion intoand out of the EC stack during tempering. In this embodiment, thediffusion barrier is substantially transparent. In one embodiment, thecapping layer includes at least one of silicon dioxide, silicon aluminumoxide, silicon nitride, and silicon oxynitride.

In one embodiment, the capping layer is a sacrificial layer. In suchembodiments, the capping layer need not be transparent because it may beremoved after and/or during the tempering process. Also, the materialfor the sacrificial capping layer may be chosen such that it is easy toremove and/or it does not adhere well to the transparent conductiveoxide used for the top electrode (for example, indium tin oxide) of theEC stack. Such materials may include silicon, titanium, and aluminum.For example, in one embodiment, the sacrificial capping layer issilicon. The silicon layer is oxidized to silicon dioxide during thetempering process. The silicon dioxide layer may be removed usingchemically selective removal, for example, hydrofluoric acid (HF) may beused to remove the sacrificial capping layer while leaving thetransparent conductive oxide substantially intact or at least infunctional form. In one embodiment, the sacrificial layer ismechanically removed. In another embodiment, the sacrificial layer isetched using a plasma. In one embodiment, the sacrificial layer isremoved by ion milling. In another embodiment, the sacrificial layer isremoved by laser ablation. In one embodiment, the sacrificial layer isremoved by exposure to irradiation, e.g., excimer laser, to maximizethermal expansion of the sacrificial layer as compared to the underlyingEC device. The sacrificial layer is thus removed by shearing forces,i.e., it peels off or breaks off in pieces as is shatters under theshearing stress imparted by the excimer laser. EC elements areparticularly well suited for methods employing shearing forces to removethe sacrificial layer, because EC elements do not have sublayers thatare subject to such shearing forces and thus more shearing force can beused to remove the sacrificial layer.

In one embodiment, the sacrificial layer blocks and/or aids inpreventing lithium from leaving the EC stack during tempering. Forexample, in one embodiment a sacrificial layer of lithium metal isdeposited on the EC stack prior to tempering. During the temperingprocess, some or all of the lithium layer is lost but it aids inpreventing the lithium in the EC device (deposited as part of the ECdevice formation) from leaving the stack during tempering. In anotherembodiment, the sacrificial layer is a lithium alloy or a lithiumintermetallic (for example, a lithium aluminum alloy or a lithiumsilicon alloy). During tempering, the alloy or intermetallic provideslithium to the device. The remaining alloy or intermetallic is removedafter tempering, for example, by plasma etching. In one embodiment, thelithium alloy or intermetallic is applied over a layer of lithium metal.

In certain embodiments, the stoichiometry of one or more of thematerials of the EC device stack is selected such that when the EC stackis exposed to the tempering process conditions, a desired stoichiometryand performance results. In one embodiment, at least one of the lithiumdose and the oxygen content are lowered in one more layers of the ECstack. In one embodiment, the lithium dose in a region that isultimately converted into a region that functions as an IC layer islowered prior to tempering. In one embodiment, the oxygen content ofwhat is normally a superstoichiometric oxygenated region is lowered to astoichiometric or sub-stoichiometric amount of oxygen. In this way,oxygen that diffuses into the EC stack during tempering is used to formthe desired stoichiometry during tempering. In one embodiment the oxygenlevels of a tungsten oxide layer are lowered.

In one embodiment, the thickness of a superstoichiometric tungsten oxidelayer is made thinner than it would have been in the absence ofprocessing under tempering conditions. This reduces the overall oxygencontent in the layer and accounts for oxygen from the ambient diffusinginto the stack during tempering.

In another embodiment, the oxygen content in one more layers of the ECstack is increased above its target value. During the tempering process,some of this excess oxygen is released from the EC stack and thisresults in the desired oxygen content following the tempering process.

In certain embodiments, at least one of the oxygen content and thelithium content of the individual layers of the EC stack are chosen sothat during the high temperatures encountered during tempering, there isminimal migration and/or redistribution of the species between thelayers. For example, during tempering lithium and oxygen are speciesthat readily diffuse through the EC stack. Depending on a particularlayer's relative ability to permit or resist diffusion of the species ascompared to other layers in the stack, there can be stresses generatedin the EC stack as the species diffuse through the EC stack, forexample, transitioning from diffusion through one material and intoanother material. Although not necessarily the best for the performancedesired in the final EC device, the oxygen and/or lithium levels in eachof the EC stack layers may be chosen such that migration and/orredistribution is minimized during tempering. The lithium and/or oxygencontent of each of the layers may not be equal prior to tempering,rather the content of each layer may be specified such that minimaldiffusion occurs during tempering. For example, lithium maypreferentially migrate toward a particular layer during heating due to agradient of lithium across two material layers. The lithium content ofeach of the layers may be selected to minimize this gradient.

In some embodiments, the glass substrate is tempered with the EC stackthereon, but under an inert atmosphere. In one embodiment, this includesinert atmosphere both during the heating stage of tempering and duringthe cooling or quenching stage of the tempering. One or more noble gasesand/or nitrogen can be used. Although not wishing to be bound by theory,it is believed that the inert gas aids in preventing species fromdiffusing out of the EC stack during tempering and/or at least protectsthe EC stack from further oxidation that would be encountered withconventional tempering where the substrate would be exposed to theambient.

Tempering of Electrochromic Devices Including Excess Lithium

In some embodiments, the damage to an electrochromic device duringtempering results, at least in part, from the loss of lithium ions orother mobile charge carriers during exposure to high temperatures. It isbelieved that the lithium may be lost to the ambient by evaporation oroxidation of lithium at the outer edges of the electrochromic device,i.e., an edge which is exposed to the ambient. Alternatively, or inaddition, some of the lithium may be lost by diffusion into the glasspane on which the electrochromic device is fabricated. Still further,some of the lithium which may actually remain within the electrochromicdevice stack during tempering may be lost by conversion of the lithiumions to lithium oxide or other compounds that effectively binds to andrenders the otherwise mobile lithium ions immobile.

To address any one or more of these various sources of lithium loss, anelectrochromic device may be fabricated with excess lithium formed in oron the device. In some embodiments, a layer of metallic lithium isfabricated within the device at a particular interface between layers ofthe stack. Thus, for example, a layer of metallic lithium may be formedbetween a transparent conducting oxide electrode and either theelectrochromic layer or the counter electrode layer. Alternatively, alayer of metallic lithium may be formed between the counter electrodelayer and the electrochromic layer or between an ion conducting layerand one or both of the electrochromic layer and a counter electrodelayer. Alternatively, the excess lithium may be provided as a metalliclayer on an outer edge of the electrochromic device prior to tempering.In other embodiments, the excess lithium is provided as excess lithiumions in a particular layer or in multiple layers of the electrochromicstack. In certain specific embodiments, the excess lithium is providedin one or both of the electrochromic layer and a counter electrodelayer. In such layers, the excess lithium may result in asuperstoichiometric lithium containing composition.

Generally, excess lithium provided in one or more regions of an ECdevice prior to tempering may be used to compensate for loss and/orconversion of lithium to a non-mobile form during tempering. However,some lithium may be converted to a non-mobile form during tempering, bydesign. For example, as described in U.S. patent application Ser. No.12/772,055, filed Apr. 30, 2010, U.S. patent application Ser. No.12/772,075, filed Apr. 30, 2010, and U.S. patent application Ser. No.13/166,537, filed Jun. 22, 2011, all of which are herein incorporated byreference, in certain embodiments, a superstoichiometric region or layeris formed in the EC device construct. Lithium interaction with thissuperstoichiometric region, for example, during heating of the deviceduring fabrication, can create an interfacial region that serves thefunction of an IC layer. Without wishing to be bound by theory, it isbelieved that at least some of the free lithium is converted to one ormore immobile lithium compounds that serve as part of a matrix of theaforementioned interfacial region which serves the function of aconventional IC layer, i.e., it is electronically insulating butionically conductive. Other portions of the lithium remain as mobilelithium ions that are active in the functioning EC device in theconventional sense, i.e., by transporting across the device duringswitching, when an electrical charge is applied to the electrodes of thedevice. Due to the higher temperatures encountered by the device duringtempering, additional lithium may be strategically placed in the devicein order to compensate for increased diffusion and or evaporation oflithium, including allowing sufficient lithium to remain in the devicein a mobile form and lithium needed to form the aforementionedinterfacial region.

The amount of excess lithium provided to the electrochromic device priorto tempering depends, in part, on the amount of lithium expected to belost during the tempering process. In some cases, the amount of excesslithium is chosen to exactly compensate for the amount of lithium thatis lost, as determined by empirical measurements or calculation. In aspecific embodiment, the amount of excess lithium is between about 10%and 500% of the amount of lithium required for a (normally) functioningelectrochromic device. That is, at least the amount of lithium requiredto satisfy the stoichiometry of the material layer that is the limitingfactor (lowest molar amount as compared to the other material layersthat switch using lithium intercalation/deintercalation) for amount oflithium needed to function. In additional embodiments, the amount ofexcess lithium is between about 25% and 250% in excess of the amountnominally required to operate the device, and in other embodiments, theamount of excess lithium is between about 50% and 100% in excess of theamount nominally required. It should be understood that the amount oflithium required for a properly functioning electrochromic device needsto account for the “blind charge” encountered in normal electrochromicdevices. Some discussion of blind charge and the amount of lithiumrequired for normally functioning devices is found in U.S. patentapplication Ser. No. 12/645,111 and U.S. patent application Ser. No.12/645,159, which were previously incorporated by reference.

Methods for Controlling the Location of Lithium in ElectrochromicDevices Prior to Thermal Tempering

In certain embodiments, the electrochromic device fabrication conditionsare modified, or a post fabrication step is performed, to direct some orall of the lithium ions within the electrochromic device to a particularlocation within that device prior to tempering. For example, it may bedesirable to drive some or all of the lithium ions into the counterelectrode layer prior to tempering. In certain embodiments, thisadditional processing to position the lithium ions is performed at apoint in the overall fabrication process after which the second of theelectrochromic and counter electrode layers is deposited. In oneembodiment, the additional processing is performed immediately after thesecond of these layers is deposited. In other embodiments, for example,the additional processing is performed upon removal of the fullyfabricated electrochromic device from the fabrication apparatus. Forexample, the additional operation may be performed after the secondtransparent conducting oxide electrode is deposited and/or after acapping layer, if any, is formed on the electrode layer.

Various techniques may be employed to direct the lithium ions into aparticular location in the device stack. For example, selective heatingof one the faces of the electrochromic device may drive lithium to adesired location within the stack. In a specific embodiment,approximately 100% of the mobile lithium ions in the device are driveninto the counter electrode layer prior to tempering.

It should be borne in mind that localizing lithium ions at a desiredlocation may be accomplished, at least in part, by controlling thecomposition of the various layers in the stack as they are deposited.For example, a nickel tungsten oxide counter electrode layer may bedeposited with a greatly enriched concentration of lithium. Theelectrochromic layer could be deposited without any lithium added. Insome embodiments, the lithium rich counter electrode layer is depositedafter the electrochromic layer in order to minimize the diffusion oflithium out of the counter electrode layer during the later stages ofthe device fabrication process.

It should also be understood that the location of the lithium ions maybe chosen to provide a sufficient distance between the ions and asurface where they may be lost. Therefore, it may be desirable to havethe lithium ions located as far away from the loss surface as possible,so that the diffusion path is sufficiently great that the lithium maynot be lost in significant quantity during tempering. For example, ifmost or all of lithium would be lost through the outer exposed surfaceof the stack, then it is desirable to have the lithium located, to theextent possible, at the position in the stack that is furthest removedfrom the outer exposed surface. In contrast, if most of the lithium islost into the glass during tempering, then prior to tempering, thenlithium is positioned as close to the outer surface of the device aspossible in order to provide a long diffusion path to the glassinterface. In some embodiments, when it is known that lithium is lostthrough both major surface areas (faces) of the electrochromic device,one may drive the lithium into the interior or central region of theelectrochromic device. For example, in one embodiment the lithium isconcentrated in a central region between the electrochromic layer andthe counter electrode layer. In one embodiment, the electrochromic layerincludes a superstoichiometric oxygenated portion. As the electrochromicdevice is heated during tempering, the lithium diffuses throughout thedevice, and a portion of the lithium interacts with thesuperstoichiometric region and forms an interfacial region, which servesthe function of an IC layer. Sufficient lithium may be deposited in thecentral region to serve this purpose, as well as to account for blindcharge, mobile lithium required for switching the device, as well asloss of lithium from the device during tempering.

Methods for Controlling the Activity of Lithium in ElectrochromicDevices During Thermal Tempering

In some embodiments, damage to a fabricated electrochromic device fromtempering can be mitigated or eliminated by controlling the chemicalactivity of the lithium in the device structure. One mechanism forreducing the chemical activity of lithium is by reducing the drivingforce for mass transport, particularly diffusion, of lithium in the hightemperatures experienced during tempering. Because diffusion of a mobilespecies such as lithium ions is driven by the size of the lithiumconcentration gradient (or more precisely the lithium ion activitygradient) within any particular layer or across layers (or regions) inthe electrochromic device structure, one method of reducing lithium ionactivity is by engineering the activity gradients of lithium ions withinthe device. With a reduction in the driving force for lithium ions toreach an outer edge of the electrochromic device (whether the exposedouter surface of the device or the interface with the glass pane at theinner side of the device), one confines the lithium to the stack andthereby reduces the lithium lost during tempering.

In one embodiment, a relatively high concentration of lithium isprovided on the outer exposed surface of the electrochromic device priorto tempering. Thus, the device will effectively have a lithiumconcentration gradient that naturally drives lithium ions toward thedevice interior and away from its exposed surface during the hightemperatures encountered with tempering. In this embodiment, some of thelithium on the outer surface is sacrificial, while some of the lithiumis not. As the lithium on the outer surface is exposed to heat duringtempering, some of the lithium evaporates while some diffuses into thedevice structure. The amount of lithium on the outer surface may be anexcess amount, as described herein. Alternatively, the higherconcentration of lithium may reside at the innermost face of the device,i.e., the side of the device that contacts the glass layer. This willpresent a concentration gradient that drives lithium away from theglass-device interface and toward the stack interior. In yet anotherapproach, relatively high concentrations of lithium are provided on bothedges of the device so that all lithium diffusion is naturally driventoward the device interior and away from the edge regions where it mightotherwise be lost to the environment. Higher concentrations of lithiumprovided in this embodiment may be made available through depositionmetallic lithium and/or a lithium compound (for example, lithiumcarbonate, lithium oxide, lithium silicate, lithium tungstate, lithiumniobate) and may include relatively high concentrations of lithium ionswithin the device layers as well.

In some embodiments, a lithium diffusion barrier is inserted at or neara surface where the lithium ions might be lost. Such diffusion barriereffectively blocks the transport of lithium ions to an edge of thedevice where they might otherwise be lost during tempering. A lithiumdiffusion barrier may be used in conjunction with one or more of theother techniques described herein. For example, a lithium diffusionbarrier at the glass-device interface, on the exposed surface of thedevice, or both, may be employed to inhibit lithium loss from the deviceduring tempering.

It should be understood that localizing some or all of the lithium ionsat a particular position within the electrochromic device (to controlthe activity gradient) may be accomplished by various techniques. Asmentioned, the lithium may be deposited at these locations duringfabrication of the device, by sputtering metallic lithium onto thedevice, or by depositing a particular material that is part of thedevice structure, where the material is particularly rich in lithium.Alternatively, the lithium may be driven to one side or the other of thestack by application of asymmetric heating, as described above.

With this in mind, the additional lithium needed to force diffusion in adirection away from a loss surface may involve depositing islands ofmetallic lithium onto a device surface, such as onto a transparentconducting oxide electrode surface on the outer surface of the device.

In certain embodiments, a lithium “source” compound is provided at ornear the outer or inner surface of the electrochromic device. Uponheating during tempering, the source material releases lithium ionswhich increases the local concentration of lithium and aids inpreventing lithium within the device from diffusing toward the locationof the source compound. Thus, loss of lithium by diffusion andultimately release into the glass or ambient is avoided duringtempering. Examples of suitable lithium source materials include lithiumcarbonate, lithium oxide, lithium silicate, lithium tungstate, and thelike. In a specific embodiment, the lithium source material is appliedonly on the outer surface of the device, i.e., the surface of the deviceexposed to the ambient.

In certain embodiments, this lithium source material is integrated intoa layer or region that would otherwise be applied to the electrochromicdevice. For example, capping layers may be applied to provide particularoptical properties (for example, an antireflective layer), to increasethe durability of the device, and/or provide a hermetic seal to thedevice. The lithium source compound may be incorporated in the cappinglayer and may be activated during tempering, producing lithium ions.This results in a local concentration gradient which promotes lithiumdiffusion away from the surface (where it might otherwise be lost) andinto the interior regions of the device.

In yet another approach, a source of lithium may be provided in anencapsulated format, effectively serving as a reservoir of lithium thatis available to control the lithium activity gradient during tempering.In a specific embodiment, the lithium source, which may be lithium metalor a lithium compound, is provided in a core-shell morphology within theelectrochromic stack. The lithium within this shell or otherencapsulating medium is released, in one embodiment, by application ofheat during the tempering process. Examples of materials that may besuitable as an encapsulating shell for a core of metallic lithiuminclude lithium carbonate, lithium oxide, lithium silicate, lithiumtungstate, lithium niobate, and the like. In another example, lithiummetal or ions are encapsulated by carbon-containing microspheres,fullerenes, and/or nanotubes, for example, all-carbon or heterocarbon/non-carbon structures (for example, carbon-siliconheterofullerenes containing lithium ions). For example, duringtempering, the lithium (metallic or ionic) may be released while thecarbon structures are burned away. In one embodiment, lithiumencapsulating silicon cage clusters are used as an encapsulated form oflithium metal or lithium ions. Metal oxides may also be used asencapsulation materials for lithium metal and/or ions. In certainembodiments, a lithium alloy and/or a lithium intermetallic is used as asource of lithium during tempering. For example, a lithium aluminumalloy or a lithium silicon alloy may be deposited in one or more regionsof the EC device as described herein. During tempering, the alloyreleases lithium to the device. For example, lithium silicon alloys maycontain about 70 atomic percent or more of lithium. When heated to hightemperatures during tempering, the lithium silicon alloy may be used asa material for controlled release of lithium into the EC device.

In yet other embodiments, the lithium activity gradient is controlled byproviding lithium metal in the vapor phase in the tempering chamber. Atsufficiently high partial pressures, the driving force for evaporationor oxidation of lithium from the stack may be reduced.

Electrochromic Device Structures for Tempering

It has been found that the high temperatures associated with temperingglass result in the materials of different layers in an EC device havinga larger grain size. In one embodiment, the grain size of one or more ofthe layers (or regions) of the EC device is smaller than it wouldtypically be in the final EC device. By starting with materials in oneor more layers having a smaller grain size, the heat associated withtempering is used to aid in transforming the one or more layers havingthe smaller grain size into a form desired in the final EC device,rather than the tempering process transforming already appropriatelysized crystallites to unacceptable crystalline forms in the one or morelayers. In one embodiment, one or more layers of the EC stack are formedin an amorphous or substantially amorphous morphology prior totempering.

In certain embodiments, smaller grain sizes and/or an amorphous state ofthe one or more layers is achieved by deposition of a layer using alower substrate temperature during deposition, and/or lower densityand/or lower energy plasma during deposition. In this way, lower densitymaterial layers and/or more amorphous layers are formed.

In certain embodiments, one or more layers of the EC stack include amaterial that is less sensitive morphologically to the heat oftempering. In one embodiment, one or more layers of the EC stackincludes a material that is crystalline, where the materialsubstantially maintains its morphology when exposed to the heat oftempering. In one embodiment, the material that is crystallinesubstantially maintains its electrochromic stack functionality beforeand after tempering.

In certain embodiments, one or more layers of the EC stack include afirst phase material and a second phase material that leads to pinningof grain boundaries in the layer. Grain boundary pinning works by thephenomenon that when a grain boundary of the first phase materialintersects with a particle of the second phase material, a certainamount of grain boundary area of the first material is removed from thesystem. In order for the grain boundary to move off the particle, thegrain boundary area that was removed must be restored and thisrestoration of grain boundary area requires additional energy. Thus,grain boundary pinning may be used to substantially maintain grain sizeand morphology during the tempering process. Grain boundary pinning maybe used to effectively set an upper limit to grain size growth duringthe tempering process. In one embodiment, there is also a third phasematerial which aids in grain boundary pinning.

In one embodiment, the second phase material is present in a lowerquantity than the first phase material, for example, the first phasematerial is doped with the second phase material. In one embodiment, thefirst phase material is tungsten oxide and the second phase material issilicon oxide dispersed in a matrix of the tungsten oxide. In oneembodiment the first phase material is between about 95% and about 99%tungsten oxide and the second phase material is between about 1% andabout 5% silicon oxide.

One potential source of damage to electrochromic devices duringtempering results from inter-layer stresses created by volumetricchanges during the tempering process. These changes result fromdiffering coefficients of thermal expansion (CTE) among the materialsused in the layers of the device. This source of degradation may beaddressed by engineering the device so that the coefficients of thermalexpansion are matched among the various layers in the device. It isbelieved, for example, that the coefficient of thermal expansion fornickel tungsten oxide (commonly used in counter electrode layers) istypically quite different from those of the transparent conductiveoxides commonly used as the device electrodes. Such transparentconductive oxides conventionally include indium tin oxide or TEC.

In one embodiment, the coefficients of thermal expansion of thematerials used in the electrochromic device are engineered to match oneanother by modifying their respective morphologies, compositions, etc.In one embodiment, the CTE's of adjoining layers are substantiallysimilar. In one embodiment, the CTE of any two adjoining material layersdoes not vary by more than about 5%, in another embodiment the CTE ofany two adjoining material layers does not vary by more than about 15%,and in another embodiment the CTE of any two adjoining material layersdoes not vary by more than about 25%. For example, an EC device may havea tungsten oxide (cathodic electrochromic material) layer on atransparent conducting layer, and a ceramic electrolyte layer on thetungsten oxide layer. One, two, or all three of the layers may bemodified (e.g. doped, sputtered to achieve a particular density/crystalpacking/amorphicity, etc.) so that the CTE's are substantially similar.One of ordinary skill in the art would recognize that CTE's may bepositive or negative, e.g., tungsten oxide has a positive CTE attemperatures up to 700° C., but at higher temperatures has a negativeCTE. Tungsten oxide can be doped with zirconium oxide to reduce the CTEto near zero or even have a negative CTE at tempering temperatures. Inone embodiment, the tungsten oxide layer's CTE is adjusted to besubstantially similar to the adjoining material layers, where theadjoining layers' CTE's are optionally adjusted. The CTE of the tungstenoxide layer in the device is substantially similar to the adjoininglayers, e.g., the transparent conducting layer and the tungsten oxidelayer's CTE's vary by 25% or less, while at the same time the ceramicelectrolyte layer and the tungsten oxide layer's CTE's vary by 15% orless. The individual layers may have positive, negative, or zero CTE'swhile still adhering to the variance described.

In other embodiments, the presence of distinct layers in the EC deviceis minimized. For example, rather than having distinct material layers,one or more graded regions exist in the EC device. In one embodiment,the entire device structure is graded, i.e., an EC element is fabricatedon a non-tempered glass substrate. The desired EC lites are cut from thesubstrate and subsequently tempered. Since there are no distinctboundaries between layers, the EC element is may be less prone to damageduring tempering. For example, a graded region with a gradual transitionfrom one material to another may be less prone to damage due todifferences in the coefficients of thermal expansion of the twomaterials. As another example, a graded region with a gradual transitionfrom one material to another may be less prone to damage due thediffusion of species (e.g., oxygen or lithium) between the materials.

Chemical Strengthening Methods

In certain embodiments, chemical strengthening is used in lieu oftempering to strengthen the glass substrate. For example, ions such asNa⁺ or K⁺ may be diffused into the surface of the glass substrate inorder to create a high stress skin layer which places the external glasssurface into compression, thereby increasing glass strength. In oneembodiment, chemical strengthening is used post EC device formation. Inone embodiment, the EC device is designed to allow for motion of theions required for chemical strengthening through the EC device withoutsubstantially changing the structure, composition, or distribution ofother ions (for example, Li⁺) present in the EC device, or in certainembodiments, the lithium or other ions are replaced in the EC deviceafter the chemical strengthening.

For example, in some embodiments, lithium or sodium aluminosilicateglass is used as a substrate for EC device fabrication. The EC device isconfigured to function using lithium ion intercalation/deintercalation.The lithium may be added to the device during fabrication or not. Afterdevice fabrication, the glass is heated in a salt bath, e.g., moltenpotassium nitrate (melting point 334° C.), containing a highconcentration of potassium ions relative to the lithium or sodium ionsin the glass. Ion exchange takes place, with lithium or sodium ions inthe glass exchanging with potassium ions, that strengthens the glass ina similar fashion to tempering, because the exchange only occurs in anouter region of the glass. This creates a compression and tension zonemuch like tempered glass, but not as strong. In the event the EC deviceloses its lithium ions during the ion exchange, the lithium ions arereplaced selectively to the EC device, leaving the glass in astrengthened form. In the event the lithium ions were not added to thedevice prior to chemical strengthening, ion exchange is selectively usedto replace any potassium ions in the device with lithium ions. Forexample, the top surface of the EC coating is treated with an excess oflithium ions. The ensuing ion exchange replaces potassium in the devicewith lithium. The device may be washed to remove excess potassiumnitrate and be further heated to remove any moisture.

In one embodiment, a layer having a high concentration of the speciesrequired for chemical strengthening (for example, Na⁺ or K⁺) isdeposited at the glass/EC stack interface. In one example, potassiumnitrate is deposited as a film on the glass. The film may be spraycoated or dipped, and then dried to remove moisture. In this embodiment,the bottom layer (e.g., a TCO layer or diffusion barrier) of the ECstack is made of a material that minimizes diffusion of the chemicalstrengthening species through it, and thus forms a barrier layer to thechemical strengthening species. The remainder of the EC device isfabricated thereon, which, e.g., is a device as described herein,including lithium. The glass is then subjected to heating, e.g., betweenabout 300° C. and about 400° C., and in one embodiment between about350° C. and about 375° C. During heating, the potassium ions willpreferentially diffuse into the glass allowing for chemicalstrengthening of the glass substrate with minimal impact to the ECdevice on top of the substrate. It is known that EC devices will notdetrimentally lose lithium at the temperatures described for theseembodiments. In certain embodiments, the EC device is lithiated afterthe heating process.

FIGS. 5A and 5B show tables summarizing some of the differentembodiments disclosed herein.

Although the foregoing disclosed embodiments have been described in somedetail to facilitate understanding, the described embodiments are to beconsidered illustrative and not limiting. It will be apparent to one ofordinary skill in the art that certain changes and modifications can bepracticed within the scope of the appended claims.

What is claimed is:
 1. A method of fabricating an electrochromic deviceon a glass substrate, the method comprising: a) forming a lithiumdiffusion barrier on the glass substrate; b) forming a first transparentconducting oxide layer on the glass substrate; c) forming a stack on thefirst transparent conducting oxide layer, the stack comprising: (i) anelectrochromic layer comprising an electrochromic material; and (ii) acounter electrode layer comprising a counter electrode material; d)introducing lithium to the stack in excess of that required for theelectrochromic device to operate in transitioning between opticalstates, wherein the lithium is introduced to the stack prior totempering; e) forming a second transparent conducting oxide layer on topof the stack of layers; and f) tempering the glass substrate afteroperation e).
 2. The method of claim 1, wherein introducing the lithiumfurther comprises depositing a layer of lithium metal on the firsttransparent conducting oxide layer, the electrochromic layer or thecounter electrode layer.
 3. The method of claim 1, wherein forming thestack further comprises forming an ion conducting layer between theelectrochromic layer and the counter electrode layer, and whereinintroducing the lithium further comprises forming a layer of lithiummetal disposed between the electrochromic layer and the ion conductinglayer, and/or the counter electrode layer and the ion conducting layer.4. The method of claim 1, wherein the excess lithium is included in theelectrochromic layer or in the counter electrode layer.
 5. The method ofclaim 1, wherein the excess lithium is included in both theelectrochromic layer and in the counter electrode layer.
 6. The methodof claim 1, wherein the excess lithium is between 10% and 500% of thatrequired for the electrochromic device to operate in transitioningbetween optical states.
 7. The method of claim 1, wherein the excesslithium is between 25% and 250% of that required for the electrochromicdevice to operate in transitioning between optical states.
 8. The methodof claim 1, wherein the excess lithium is between 50% and 100% of thatrequired for the electrochromic device to operate in transitioningbetween optical states.
 9. The method of claim 1, wherein lithium isintroduced such that the electrochromic layer includes substantially nolithium, and the counter electrode layer includes lithium.
 10. Themethod in claim 9, wherein the electrochromic layer is formed before thecounter electrode layer is formed.
 11. The method of claim 1, furthercomprising forming a capping layer on the second transparent conductingoxide layer, and wherein the capping layer is configured to reducelithium diffusion from the electrochromic device during tempering. 12.The method of claim 11, wherein the capping layer includes at least oneof lithium metal and a lithium intermetallic.
 13. The method of claim 1,wherein fabricating the electrochromic device includes forming theelectrochromic layer and/or the counter electrode layer including aspecific stoichiometry of oxygen and/or lithium, and wherein temperingthe glass substrate causes the oxygen and/or lithium in theelectrochromic device to diffuse in the electrochromic device to form afunctional electrochromic device configured to operate in transitioningbetween optical states.
 14. A method of fabricating an electrochromicdevice on a glass substrate, the method comprising: a) forming a lithiumdiffusion barrier on the glass substrate; b) forming a first transparentconducting oxide layer on the glass substrate; c) forming a stack on thefirst transparent conducting oxide layer, comprising: (i) forming anelectrochromic layer comprising an electrochromic material, wherein theelectrochromic layer is formed to include a superstoichiometricoxygenated region of the electrochromic material; and (ii) forming acounter electrode layer comprising a counter electrode material; d)forming a second transparent conducting oxide layer on top of the stack;e) providing lithium ions in the electrochromic device; f) driving thelithium ions in the electrochromic device into the electrochromic layer,the counter electrode layer, and/or a region between the electrochromiclayer and the counter electrode layer; and, g) after driving the lithiumions, tempering the glass substrate.
 15. The method of claim 14, whereinthe lithium ions are driven into the counter electrode layer.
 16. Themethod of claim 15, wherein 75% to 100% of the lithium ions are driveninto the counter electrode layer.
 17. The method of claim 14, whereindriving the lithium ions is performed after forming the electrochromiclayer or the counter electrode layer.
 18. The method of claim 14,wherein driving the lithium ions is performed after removing the glasssubstrate from an electrochromic device fabrication apparatus.
 19. Themethod of claim 14, wherein driving the lithium ions is performed byheating the electrochromic layer or the counter electrode layer.
 20. Themethod of claim 14, wherein driving the lithium ions is performed byapplying voltage or current to the first and the second transparentconducting oxide layers.
 21. A method comprising: fabricating anelectrochromic device disposed on a glass substrate; providing a lithiumsource disposed on a surface of the electrochromic device; and temperingthe glass substrate after fabricating the electrochromic device on theglass substrate.
 22. The method of claim 21, wherein lithium from thelithium source diffuses into the electrochromic device during temperingthe glass substrate.
 23. The method of claim 21, wherein the lithiumsource is provided on an exposed surface of the electrochromic device.24. The method of claim 21, wherein the lithium source is providedbetween the glass substrate and the electrochromic device by depositingthe lithium source on the glass substrate and then fabricating theelectrochromic device on the lithium source.
 25. The method of claim 21,wherein the lithium source is provided on edges of the electrochromicdevice.
 26. The method of claim 21, wherein the lithium source includesmetallic lithium and/or a lithium compound.
 27. The method of claim 26,wherein the lithium compound includes at least one of lithium carbonate,lithium oxide, lithium silicate, lithium tungstate, and lithium niobate.28. The method of claim 21, wherein the electrochromic device includeslithium apart from that supplied from the lithium source.
 29. The methodof claim 11, wherein the capping layer is a sacrificial layer.
 30. Themethod of claim 29, wherein the capping layer comprises at least one ofsilicon, titanium or aluminum.
 31. The method of claim 30, furthercomprising removing the capping layer after tempering the glasssubstrate.